1. Technical Field
The present invention relates to an activated carbon/NiO/ZnO and an activated carbon/ZnO composite, a method in which the composites are obtained, and a method in which the composites are used as adsorbents in a method of desulfurization of diesel fuel.
2. Description of the Related Art
The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.
The demand for transportation fuels has been increasing in most countries for the past two decades, and the diesel fuel demand is expected to increase significantly in the early part of the 21st (A. Brady, Buoyant Later Next Decade, Oil Gas J., 97, 75-80, 1999-incorporated herein by reference in its entirety). The main goal of policymakers is to produce transportation fuels that have a sulfur content below 10 parts per million (ppm). The next step, which has already begun in a number of countries, is the extension of stricter sulfur specifications beyond on-road transportation to other products, particularly fuel oil, marine bunkers and jet fuel (OPEC Secretariat, Helferstorferstrasse 17 A- 1010 Vienna, Austria, 2011 www.opec.org—incorporated herein by reference in its entirety). Sulfur compounds present in fuels lead to the emission of sulfur oxide gases (SOx). These gases react with water in the atmosphere to form sulfates and acid rain which damages buildings, destroys automotive paint finishes, acidifies soil, and ultimately leads to loss of forests and various other ecosystems (W. L. Fang, Inventory of U.S. 1990-2003, Clean Air Markets Division, 2004.—incorporated herein by reference in its entirety).
Traces of sulfur present in diesel fuels also poison the catalysts in the emission control system and reduce their effectiveness for the oxidation of harmful carbon monoxide, hydrocarbons and volatile organic matter. Sulfur emissions also cause several human health concerns such as, respiratory illnesses, aggravate heart disease, trigger asthma, and contribute to formation of atmospheric particulates (V. C. Srivastava, RSC Advances, 2, 759-783, 2012—incorporated herein by reference in its entirety), global warming and water pollution (S. F. Vernier, EU environmental laws impact fuels' requirements, Hydrocarbon Process, 79, 51-71, 2000.—incorporated herein by reference in its entirety). Environmental regulations have been introduced in many countries around the world to reduce the sulfur content of diesel fuel to ultra-low levels of 10 ppm with the aim of lowering the diesel engine's harmful exhaust emissions and improving air quality (US EPA, EPA420-F-99-011, Office of Mobile Sources, May 1999.—incorporated herein by reference in its entirety). Therefore, desulfurization of fuels is extremely important in the petroleum industry and there is a need to research new desulphurization methods which are cost effective, more efficient and can meet the environmental regulations and refining requirements.
The current industrial method for removal of sulfur from fuels is (HDS), for reducing of organic-sulfur in gasoline, diesel and other intermediate distillates where Co—Mo/Al2O3 or Ni—Mo/Al2O3, Ni—W/Al2O3 is used as the catalysts for the conversion of organic sulfur toH2S. This process successfully removes many sulfur compounds such as thiols, sulfides, disulfides and some thiophene derivatives, but to much lower extent removes dibenzothiophene derivates due to the steric hindrance on the sulfur atom (refractory organosulfur compounds), such as dibenzothiophene (H. Schulz, et al., Fuel Process Technol., 61, 5-41, 1999; H. Schulz, et al., Catal. Today, 49, 87-97, 1999—each incorporated herein by reference in its entirety).
Adsorption is often employed to remove trace impurities, such as the removal of trace amounts of aromatics from aliphatic (R. T. Hernandez et al., US patent 2004/0040891 US 2004/0044262 A1. 2004—incorporated herein by reference in its entirety) and it is the most common HDS alternative method currently used to achieve ultra-clean fuels (M. Tymchyshyn, Lakehead University, 2008.—incorporated herein by reference in its entirety). Adsorptive desulfurization using porous materials is considered to be an efficient and economical way for removing organosulfur compounds due to its low-energy consumption, the ambient operation temperature and atmospheric pressure without using pressurized hydrogen gas and the availability of regeneration of the spent adsorbent and broad availability of adsorbents (Q. Wang, et al., Fuel Processing Technology, 90, 381-387, 2009.—incorporated herein by reference in its entirety). Activated carbon (AC) is one of the most important adsorbents dominating the commercial use of adsorption due to its porous structure with high surface area, large pore volume and they have high efficiency for the adsorption of various types of compounds (M. Suzuki, Adsorption Engineering, Kodansha Ltd., Tokyo, 1990.—incorporated herein by reference in its entirety). It was found that activated carbon was the best adsorbent between the activated alumina and nickel-silica alumina to remove model sulfur compounds from n-hexadecane (J. H. Kim, et al., Catal. Today, 111, 74-83, 2006—incorporated herein by reference in its entirety).
Salem and Hamid (K. Tang, et al., Fuel processing Technology, 89, 1-6, 2008-incorporated herein by reference in its entirety) studied removing of sulfur from naphtha with a 550 ppm initial sulfur level in a batch reactor using activated carbon, zeolite 5A, and zeolite 13X as solid adsorbents. They reported that, Activated carbon showed the highest capacity, but a low level of sulfur removal. Activated carbon was found to have much better adsorption characteristics than 13X type zeolite (M. Muzica, et al., Chemical engineering research and design, 88, 487-495, 2010—incorporated herein by reference in its entirety). Bu et al. Studied the Adsorptive affinity of polycyclic aromatic sulfur heterocycles (PASHs) and polycyclic aromatic hydrocarbons (PAHs) on commercial activated carbons AC1- to AC7. They concluded that the adsorption selectivity increases as follows: naphthalene<fluorene<dibenzothiophene<4,6-dimethyl dibenzothiophene<anthracene<phenanthrene (J. Bu et al., Chemical Engineering Journal, 166, 207-217, 2011—incorporated herein by reference in its entirety).
Granular activated carbon (GAC) was produced from dates' stones by chemical activation using ZnCl2 as an activator. GAC samples were used in desulfurization of a model diesel fuel composed of n-decane and dibenzothiophene (DBT) as sulfur containing compound. More than 86% of DBT is adsorbed in the first 3 h which gradually increases to 92.6% in 48 h and no more sulfur is removed thereafter (Y. A. Alhamed, et al., Fuel, 88, 87-94, 2009—incorporated herein by reference in its entirety).
Study was employed for sulfur removal from model oil (dibenzothiophene; DBT dissolved in iso-octane) using commercial activated carbon (CAC) as an adsorbent. The highest removal of sulfur by CAC was obtained with adsorbent dosage 20 g/L, time of adsorption 6 h, and temperature 308° C.) (D. R. Kumar, et al., Air, Water, 40, 545-550, 2012-incorporated herein by reference in its entirety).
Recently, four types of carbons (activated carbon, Maxsorb superactivated carbon, mesoporous templated carbon CMK-3, and graphene) were investigated as selective sorbents for adsorption of thiophene from its solution in n-octane.
The adsorption capacities for thiophene followed the order: graphene>CMK-3>Maxsorb>AC. Surface area is not a critical factor influencing sulfur capacity of carbon sorbents in addition, the carbene-type zigzag edge sites and the carbyne-type armchair edge sites on graphene are among the possible sites for strong interactions with thiophene (L. Wang et al., AIChE Letter: Separations: Materials, Devices and Processes, 59, 29-32, 2013—incorporated herein by reference in its entirety).
Modifications of carbon surfaces by incorporation of metals and oxidation of carbon surface can have a positive effect on the adsorption of DBTs. Jiang et al found that, the modified activated carbon by concentratedH2SO4 at 250° C. has much higher adsorption capacities for dibenzothiophene than the unmodified AC but less adsorption capacities for small molecules (e.g., iodine) (Z. Jiang, et al., Langmuir, 19, 731-736, 2003—incorporated herein by reference in its entirety). It was also reported that cobalt and copper loaded carbons showed the highest uptake, due to not-well defined catalytic synergistic effects (C. O. Ania, et al., Carbon, 44, 2404-2412, 2006—incorporated herein by reference in its entirety). Adsorption Desulphurization of Gasoline by Silver loaded onto modified Activated Carbons was studied by Cao, et al. The results showed that silver formed π-complexes with organic sulphides; the higher the silver loading, the greater the amount adsorbed, but the adsorption selectivity was poor (B. Cao, et al., Adsorpt. Sci. Technol., 26, 595-609, 2008—incorporated herein by reference in its entirety).
The adsorption of benzothiophene and dibenzothiophene on transition-metal ionimpregnated activated carbons is investigated (Xiao et al., Energy & Fuels, 22, 3858-3863, 2008—incorporated herein by reference in its entirety) and the equilibrium amounts adsorbed of BT and DBT on the modified ACs followed the order: AgI/AC>NiII/AC>CuII/AC>ZnII/AC>AC>FeIII/AC. Zhou et al, reported that HNO3oxidation of AC was an effective method for improving adsorption performance of sulfur compounds, due to an increase in the acidic oxygen-containing functional groups, suggesting that the adsorption of sulfur compounds over the AC may involve an interaction of the acidic oxygencontaining groups on AC with the sulfur compounds (A. Zhou, et al., Appl. Catal., B, 87, 190-199, 2009—incorporated herein by reference in its entirety). Two commercially available activated carbons A and B and modified forms of the same by HNO3 treatment and Ni supported systems were used as adsorbents for, 4-methylbenzothiophene and 4,6-dimethyl-dibenzothiophene in Adsorptive desulfurization (ADS) process. The results showed that, the trend for adsorption selectivity for various adsorbents increases in the order, carbon A (modified)>carbon B (modified)>Ni/carbon A>Ni/carbon B>Ni/silica>Ni/alumina>Ni/HY-zeolite (V. Selvavathi et al., Catalysis Today, 141, 99-102, 2009—incorporated herein by reference in its entirety). Zirconium dioxide was impregnated into a commercial activated carbon (AC) and tested as adsorbents for dibenzothiophene (DBT) from a model diesel fuel. The results indicated that surface acidic sites on the impregnated ZrO2 may play an important role in the improved desulphurization performance of the composite (L. Xiong, et al., Adsorpt. Sci. Technol., 28, 341-350, 2010—incorporated herein by reference in its entirety). Cerium-loaded activated carbon was tested for dibenzothiophene adsorption from model fuels. This adsorbent showed much better adsorption capacity and selectivity towards DBT than the virgin carbon due to the changes in surface chemistry of the adsorbent, in which the increased acidic sites and cerium ion may play important roles (L. Xiong, et al., Porous Mater 19, 713-719, 2012—incorporated herein by reference in its entirety).
The need for cleaner burning fuels has resulted in a continuing world-wide effort to reduce sulfur levels in hydrocarbon-containing fluids such as gasoline and diesel fuels. The reduction of sulfur in such hydrocarbon-containing fluids is considered to be a means for improving air quality because of the negative impact the sulfur has on the performance of sulfur-sensitive items such as automotive catalytic converters. The presence of oxides of sulfur in automotive engine exhaust inhibits and may irreversibly poison noble metal catalysts in the converter. Emissions from an inefficient or poisoned converter contain levels of non-combusted, non-methane hydrocarbons, oxides of nitrogen, and carbon monoxide. Such emissions are catalyzed by sunlight to form ground level ozone, more commonly referred to as smog.
Most of the sulfur in a hydrocarbon-containing fluid such as gasoline comes from thermally processed gasolines. Thermally processed gasolines such as, for example, thermally cracked gasoline, visbreaker gasoline, coker gasoline and catalytically cracked gasoline (hereinafter collectively referred to as “cracked-gasoline”) contains, in part, olefins, aromatics, sulfur, and sulfur-containing compounds.
Since most gasolines, such as for example automobile gasolines, racing gasolines, aviation gasolines, boat gasolines, and the like contain a blend of, at least in part, cracked-gasoline, reduction of sulfur in cracked-gasoline will inherently serve to reduce the sulfur levels in most gasolines such as, for example, automobile gasolines, racing gasolines, aviation gasolines, boat gasolines, and the like.
The public discussion about gasoline sulfur has not centered on whether or not sulfur levels should be reduced. A consensus has emerged that lower sulfur gasoline reduces automotive emissions and improves air quality. Thus, the real debate has focused on the required level of reduction, the geographical areas in need of lower sulfur gasoline, and the time frame for implementation.
As the concern over the impact of automotive air pollution continues, it is clear that further efforts to reduce the sulfur levels in automotive fuels will be required. While the current gasoline products contain about 330 parts per million (ppm), the U.S. Environmental Protection Agency recently issued regulations requiring the average sulfur content in gasoline to be less than 30 ppm average with an 80 ppm cap. By 2006, the standards will effectively require every blend of gasoline sold in the United States to meet the 30 ppm level.
Desulfurization preferably has a minimal effect on the olefin content of such fuels so as to maintain the octane number (both research and motor octane number). Such a process would be desirable since saturation of olefins greatly affects the octane number. Such adverse effect on olefin content is generally due to the severe condition normally employed, such as during hydrodesulfurization, to remove thiophenic compounds (such as, for example, thiophenes, benzothiophenes, alkyl thiophenes, alkylbenzothiophenes, alkyl dibenzothiophenes and the like) which are some of the most difficult sulfur-containing compounds to be removed from cracked-gasoline. In addition, there is a need to avoid a system wherein the conditions are such that the aromatic content of the cracked-gasoline is also lost through saturation. Thus, there is a need for a process wherein desulfurization is achieved and the octane number is maintained.
There is also a need to reduce the sulfur content in diesel fuels. In removing sulfur from diesel fuels by hydrodesulfurization, the cetane is improved but there is a large cost in hydrogen consumption. Such hydrogen is consumed by both hydrodesulfurization and aromatic hydrogenation reactions.
Conventional desulfurization requires a significant consumption of hydrogen and has poor economical performance process for the treatment of cracked gasolines and diesel fuels.
As a result of the lack of success in providing a successful and economically feasible process for the reduction of sulfur levels in cracked-gasolines and diesel fuels, it is apparent that there is still a need for a better process for the desulfurization of such hydrocarbon-containing fluids which has minimal effect on octane levels while achieving high levels of sulfur removal. Traditionally, sorbent compositions used in processes for the removal of sulfur from hydrocarbon-containing fluids have been agglomerates utilized in fixed bed applications. Because of the various process advantages of fluidized beds, hydrocarbon-containing fluids are sometimes used in fluidized bed reactors. Fluidized bed reactors have advantages over fixed bed reactors such as better heat transfer and better pressure drop. Fluidized bed reactors generally use reactants that are particulates. The size of these particulates is generally in the range of about 1 micron to about 1000 microns. However, the reactants used generally do not have sufficient attrition resistance for all applications. Consequently, finding a sorbent with sufficient attrition resistance that removes sulfur from these hydrocarbon-containing fluids and that can be used in fluidized, transport, moving, or fixed bed reactors is desirable and would be of significant contribution to the art and to the economy.